Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-12-03
2004-09-28
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S010000, C429S006000, C429S006000
Reexamination Certificate
active
06797420
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electric power generator including a hydrogen generator and a polymer electrolyte fuel cell. More specifically, the present invention relates to an electric power generator, which uses a residual fuel gas exhausted from a fuel electrode of the fuel cell and/or an incompletely generated gas exhausted from the hydrogen generator not having a desired composition as a part of a burning fuel gas for heating the hydrogen generator.
BACKGROUND ART
(1) Electric Power Generator
A conventional electric power generator using a polymer electrolyte fuel cell will be described with reference to FIG.
3
. In a polymer electrolyte fuel cell
1
, an air electrode
2
and a fuel electrode
3
are disposed so that they sandwich a polymer electrolyte membrane
9
(for example, Nafion 117 manufactured by Du Pont). To the upstream side of the air electrode
2
, a fan
4
for supplying the air is connected, and to the upstream side of the fuel electrode
3
, a hydrogen generator
6
is connected via a switching valve
5
. A burner
7
is provided adjacent to the hydrogen generator
6
and the hydrogen generator
6
is heated with heat generated in the burner
7
. In the upstream side of the burner
7
, a burning fuel flow rate controlling valve
8
is disposed.
When a raw material fuel such as natural gas or methanol and a raw material water necessary for the steam reforming reaction are supplied to the hydrogen generator
6
and a burning fuel is supplied to the burner
7
via the burning flow rate controlling valve
8
, the temperature of the hydrogen generator
6
is increased to a predetermined temperature with a burning heat generated in the burner
7
. Hydrogen gas generated in the hydrogen generator
6
is not necessarily a pure hydrogen gas and may contain impurity gases such as carbon monoxide and carbon dioxide, and therefore it is sometimes called hydrogen rich gas. In a gas generated when the temperature of the hydrogen generator
6
is outside the predetermined temperature range, a large amount of poisoning components such as CO is contained, and this gas is exhausted from the hydrogen generator
6
as an incompletely generated hydrogen rich gas which does not have a desired composition. This incompletely generated gas is not supplied to the fuel electrode
3
but exhausted to the outside via the switching valve
5
.
When the temperature of the hydrogen generator
6
is increased to a predetermined temperature and a hydrogen rich gas having a desired composition is obtained, this is supplied to the fuel electrode
3
by operating the switching valve
5
. Then, the polymer electrolyte fuel cell
1
starts electric power generation. Most of the hydrogen in the hydrogen rich gas supplied to the fuel electrode
3
is consumed in the electric power generation and the gas containing residual hydrogen is exhausted outside as a residual fuel gas from the fuel electrode
3
.
In this manner, in the conventional electric power generator using a polymer electrolyte fuel cell, when the temperature of the hydrogen generator
6
is not in the predetermined temperature range, a large proportion of impurity gas other than hydrogen is contained in the generated gas, so this cannot be used as a fuel for the fuel electrode and is exhausted outside as an incompletely generated gas. As a consequence, there has been the problem that this incompletely generated gas might possibly catch fire with some fire source.
Further, the residual fuel gas exhausted from the fuel electrode
3
contains hydrogen that has not been consumed in the electric power generation. Consequently, the residual gas may also possibly catch fire with some fire source. Moreover, even if the residual fuel gas does not catch fire, there has been the problem that the operation efficiency of the electric power generator is decreased since a part of the hydrogen generated in the hydrogen generator is exhausted outside.
In this regard, the present invention has an object (first object) to solve the above-described problems that the prior art presents and to provide an electric power generator which does not exhaust outside the off gas containing hydrogen as it is, which does not have any possibility of inappropriately catching fire, and which have a high operation efficiency.
On the other hand, the hydrogen generator used in the electric power generator as above generates hydrogen using hydrocarbons such as natural gas, LPG, gasoline, naphtha, kerosene and methanol, water and the air. This is because hydrogen attracts attention as a prospective energy source substituting for fossil fuels.
In order to utilize hydrogen effectively, it is necessary to provide infrastructure such as hydrogen pipelines. As a method for providing such facilities, it is studied to use infrastructure which has already been built for transportation and conveyance of fossil fuels such as natural gas and fuels such as alcohol, and to reform the above fuels to generate hydrogen in the place where hydrogen is needed. For example, there have been a variety of propositions with regard to on-site electric power generator of medium and small size, namely, a technique of reforming natural gas (city gas) for fuel cells and a technique of reforming methanol for fuel cells as a power source for automobiles.
In order to reform the above fuels to generate hydrogen, a catalytic reaction at a high temperature is used, and typically, a steam reforming method, and an auto-thermal method using both a steam reforming and a partial oxidation together are used.
However, since a reforming reaction proceeds at a high temperature, an obtained reformed gas contains not only hydrogen but also carbon monoxide (CO) and carbon dioxide (CO
2
) as by-products through reaction equilibrium. When the reformed gas is used in a fuel cell, particularly in a polymer electrolyte fuel cell, CO as a by-product poisons electrodes of the fuel cell and significantly deteriorate the performance thereof. For this reason, it is necessary to reduce the concentration of CO and CO
2
in the reformed gas to the lowest possible. For this purpose, in general, a modifying reactor for shift-react CO and water, and a CO purifier using CO oxidation method or methanation method are equipped downstream side of the reforming reactor to reduce the CO concentration in the reformed gas as low as several tens of ppm. Although the CO concentration of the reformed gas is around 10%, the CO concentration of a modified gas obtained after the reformed gas passes through the shifter is reduced to around 1%. Further, the CO concentration of a purified gas obtained after the modified gas passes though the CO purifier is reduced to several tens of ppm and this is supplied to the fuel cell.
Herein, specific catalytic temperatures in the reforming reaction, modifying (shift) reaction and CO purifying reaction are 650 to 750° C., 200 to 350° C. and 100 to 200° C., respectively. In particular, if the temperature of the purifier does not reach the temperature range, the CO concentration cannot be reduced to several tens of ppm and the obtained purified gas cannot be supplied to the fuel cell. As a consequence, the starting time of the fuel cell depends on the start-up time of the catalytic temperature of the purifier. Also, the temperature of the modifying catalyst contained in the shifter reaches the active temperature with waste heat after the termination of the reforming reaction, and the modifying reaction starts. Moreover, the temperature of the purifying catalyst contained in the CO purifier reaches the active temperature with waste heat after the termination of the modifying reaction, and the modifying reaction starts.
However, in some operation method, condensed water generated in the reaction in the reformer, shifter and purifier stays inside the gas pathway and this may delay the start-up time before the respective catalytic temperatures reach the predetermined temperatures. For example, when the operation is stopped after a short time has passed from the start of operation of the hydro
Asou Tomonori
Kitagawa Koichiro
Maenishi Akira
Miyauchi Shinji
Ozeki Masataka
Parsons Thomas H.
Ryan Patrick
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